Cobalt base alloy composition



Patented May 10, 1949 COBALTBASE l z ie comosirion Hugh's. Cooper, Cleveland, Ohio No'Drawing. Application June12-, 1945,a Serial No. 599,122

fiCl'aims. 1

This invention relates to valloy compositions of matter and has for its object the provision of a rust and corrosion resistant alloy capable of being precipitation hardened to high hardness with great strength adapting the same to wide utility in the art.

Another object is to provide an alloy composition especially adapted for wide utility in the art of forming and shaping metallic and nonmetallic materials.

Still another object is to provide an alloy composition adapted for useinswaging and drawing dies.

A further object is .to provide an alloy composition adapted for'su'ch special service uses as valve seats, cutlery, surgical instruments, springs for high temperature service use, hard surfacing material, punches, drills, gauges, etc.

Other objects will be apparent as the invention is more fully hereinafter disclosed.

In accordancewith these objects I have discovered that an alloy, consisting of about 80% cobalt balance tungstenand molybdenumeach within the range 9 to 11% and inversely proportioned to each other to total 20%, possesses in addition to the properties of rust and corrosion resistance and the property of being precipitation hardenable, the; unexpected property of a relatively high modulus of transverse rupture with high hardness, which adapts the alloy to wide utility in the art of molding and shaping metallic and non-metallic materials.

Heretofore' in the art, as disclosed by Sykes Patent No. 2,050,865 (August 11, 1936) cobalttungsten alloys have been proposed in which the tungsten content is within the-range 20 to 35%. These alloys are identified as being precipitation hardenable to high hardness and to a transverse strength of about 180,000 to about 200,000'pounds per square inch.-

Heretofore in the art, also, (as disclosed by Koster Patent No. 1,949,313 "(February 2'7, 1934) cobalt-molybdenum alloys have been proposed in which the molybdenum content is within the range to 35%. These alloys,- also, are identified as being precipitationhardnable, but the strength properties of't-he-aIlOysare not mentioned.

My investigations have demonstrated that whereas the cobalt-moylbdenum alloys are precipitation h'ardenable to relativelybhigh hardness, the strength'characteristics of the alloys are relatively low and about half that obtainable with alloys of cobalt and tungsten using the same percentage amountxof tungsten instead of molyb denum.

However, my investigations have demonstrated that when molybdenum and tungsten a in total amount approximating .20 with each metal being inversely proportioned within therange 9 to 11%, but pre'ierablyxeaeh approiiirnatinghmvt; is employed, the strength of the alloy is double that obtained-With theseihe amouhtor .tunsten and about three timesth'at obtaihedWithLthesalhe amount of molybdenum withcut anysubstantial loss in hardness.

'As an illustration ofitliisg antalloy containing 20% W, balance Co, maybeprecipitation hard ened to a Brinell" hardness. oflabout'60o andea modulus of transverse rupture or about 100,000. in contrast t6 this, an alley-containing,10%"W, 10% Mo, balance Co, b may. be. precipitation hardened to a Brihellihardhessei.eboutgt'zs and a modulus oftr'ansver'se rupture ofab'o'ut 325,000 pounds per square men.

This relative proportionihg of W to Mo appears critical to the obtainahce of such high strength" allo ys', inasmuch as alloys with: a tuna sten content of. "11%" and a molybdenum content or 9% consistently, show a ewel "hardness (525 Brinell) and a lower. strength: (250,000 p. s. i.) and alloys with" a tungsten contntoi 9% and a molybdenum: conteht'of=1'1%iconsist enuy Show a higher hardness 'Brineni iwith a'lower strength" (275; 000p. s; i.)-;

The alloycomposition of the present invention, preferably is madeby-ferining'a molten iiietal bath consistingr'of substantially; pure: cobalt in which the desired amounts of tungsten and molybdenum, each within the-range 9'to 11%but in total amount approximating-20%, are dissolved.

To produce sound. castings oi the molten alloy, I have foundrlt advantageous: and desirable to add to theinolt'en alloyybeiore castinggmanganese in an amount providinggnot over 1%Mnin the cast metal andsiii'con'in an amount providing' not more than .50%'"in the cast metal.

The melting point of these alloys approximate 1400 c; and themelt's when'ueoxidizedwith Mn and" Si, are-:free :flowin'g'endhave excellent casting properties. I

The cast allom'when-alr-cooleu to atmospheric temperatures, is relatively. soft and strong and may: be mechanicallyydeiormedin: the cold by usual working methods andiwith" intermittent annealings to temperatures 50=100"below" the melting point followed by air cooling, to sub- I 3 stantially any desired configuration, section or diameter.

Before precipitation hardening the finished product, the cold worked metal must be annealed for an extended time interval at a temperature just below its melting point followed by rapid cooling to atmospheric temperatures, to condition the alloy for precipitation hardening heattreatment.

Precipitation hardening may be obtained by heatingthe quenched or rapidly cooled product for an extended time interval at a temperature within the range 400700 C. The time interval of heating may be varied somewhat to obtain variations in hardness within the range 500 to 700 Brinell. Generally this hardness range is obtained within the time interval of from 48 to 96 hours. As the hardness increases within the range 500 to 700 Brinell the transverse strength of the alloy decreases from a maximum of about 325,000 p. s. i. to a minimum of about 250,000 p.s i. Alternatively, the alloy composition of the present invention may be made by powder metallurgy methods without essential departure from the present invention. Due, however, to the difiaculty of obtaining high density sintered products by powder metallurgy methods, I prefer to form the alloy by the melting method above described.

The alloy of the present invention takes a very high polish and remains untarnished indefinitely in ordinary air. The alloy is also resistant to many types of corrosion to which most hard,high strength alloys. have been found subject. The alloy of the present invention also has been found' to retain its hardness and high strength characteristics at red heat.

The physical properties of the alloy composition of the present invention adapt the alloy to many difierent'use's, including cutting tools particularly for the softer metals, wire drawing dies, swaging dies, extrusion dies, molding dies for metals and non-metals, cutlery, drills, punches, measuring gauges, valve seats, springs, and surfacing material for wear-resistant purposes.

As an illustration of the utility of the alloy composition of the present invention, the adaptation of the same to drawing dies will be described. In the art of drawing metal wire and rods, drawing dies are employed having a tapered opening therethrough, through which the metal wire or rod is drawn, thereby reducing the diameter of the wire or rod, In such dies, it is essential that the material comprising the die'possess in addition to'high hardness resisting surface Wearing, the property of high strength, resisting transverse rupture. The alloy of the present invention is admirably well suited for use in such drawing dies and my tests have shown that dies comprised of the alloy of the present invention are markedly superior to dies comprised of cemented tungsten carbide, the material generally considered the best materialf or this purpose.

In the manufacture of such drawing dies, the best practice appears to be to first form from the cast alloy produced as above disclosed, by alternate cold working and annealing, a rod of the alloy having a diameter approximating the diameter desired in the die from which rod sections of the approximate desired die thickness may be cut.

The rod sections are then machined and provided with the desired sized tapered openings therethr'ough following which operation they are 4 precipitation hardened by heat-treatment at about 600 C. for about 96 hours to develop therein the maximum hardness. Following heat-treatment the die surfaces are ground and polished to smooth surface with simultaneous sizing of the opening therethrough and are ready for use.

Alternatively the dies may be formed by standard powder metallurgy practices, if so desired. The working characteristics of the cast alloy, however, are such that in general I prefer to employ the cast alloy in the forming of most articles comprised of this alloy.

From the above disclosure it is believed apparent that the invention may be adapted to use in a wide plurality of different fields and that a large number of different articles may be comprised of the alloy, All such modifications and adaptations of the present invention are contemplated as may fall within the scope of the following claims.

What I claim is:

1. An alloy consisting of from 9 to 11% tungsten, 11 to 9% molybdenum, the total amount of tungsten and molybdenum approximating 20%, balance cobalt.

2. A cast alloy consistin of from 9 to 11% tungsten, 11 to 9% molybdenum, the total amount of tungsten and molybdenum approximating 20%, not over 1% manganese, not over .50% silicon, balance cobalt.

3. An alloy consisting of 10% tungsten, 10% molybdenum, balance cobalt.

4. A cast alloy consisting of 10% tungsten, 10% molybdenum, not over 1% manganese, not over .50% silicon, balance cobalt.

5. Articles of manufacture comprised of an alloy consisting of from 9 to 11% tungsten, 11 to 9% molybdenum, the total amount of tungsten and molybdenum approximating 20%, balance cobalt, said alloy being in a precipitation hardened condition.

6. Articles of manufacture comprised of an alloy consisting of from 9 to 11% tungsten, 11 to 9% molybdenum, the total amount of tungsten and molybdenum approximating 20%, not over 1% manganese, not over .50% silicon, balance cobalt, said alloy being in a precipitation hardened condition.

HUGH S. COOPER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Grossman: Article in Trans, Amer. Inst. of Mining and Metallurgical Engrs, vol. 150, 1942, page 227. 

